Recovery of hydrocarbons by in situ combustion



United States Patent Office 3,@7Z,Il% Patented .lian. 8, 1953 3,072,186 RECOVERY OF HYDROCARBONS BY KN SETU COMBUSTKON Harry W. Parker, Eartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Aug. 11, 1958, Ser. No. 754,158 6 (Ilaims. (Cl. 166-411) This invention relates to a process for producing hydrocarbons from a carbonaceous stratum by in situ combustion.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material 15 becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move thru the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein, followed by injection of air thru the ignition borehole and recovery of product hydrocarbons and combustion gas thru another borehole in the stratum, is a direct air drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum usually plugs in front of the combustion zone because a heavy viscous liquid bank of hydrocarbon collects in the stratum in advance of the combustion zone which prevents movement of air to the combustion process. T o overcome this difiiculty and to permit the continued progress of the combustion zone thru the stratum, inverse air injection has been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes.

in situ combustion techniques are being applied to tar sands, shale, Athabasca sand and other strata in virgin state, to coal veins by fracturing, and to strata partially depleted by primary and even secondary and tertiary recovery methods.

In moving a combustion front thru a carbonaceous straturn, the rate of production of hydrocarbons therefrom is dependent to a considerable extent upon the rate of movement of the front thru the stratum. Any increase in the rate of advance of the combustion front is a material aid in the in situ combustion process. Another factor involved in the economics of the process is in the residual temperature of the stratum after the combustion front has passed thru. Obviously the lower the final temperature of the stratum, the less energy lost to the stratum both by transfer of heat to adjacent strata and by residual heat left in the burned out stratum to be dissipated.

Accordingly, it is an object of the invention to provide an improved process for recovering hydrocarbons from a carbonaceous stratum by in situ combustion. Another object is to increase the rate of movement of a combustion front thru a stratum during production thereof by in situ combustion. A further object is to decrease the combustion temperature in the advancing combustion zone during the in situ combustion process. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises feeding a mixture of O -containing gas and a low ignition point fuel into a combustion zone in a carbonaceous stratum with an excess of relative to the injected fuel so as to move the combustion zone thru the stratum countercurrently to the movement of the gases injected into the combustion zone. The (D -containing gas is preferably air or oxygen-enriched air. The air and fuel may be admixed prior to injection into the stratum or they may be separately injected into the stratum thru separate boreholes spaced conventional distances from the ignition or production borehole. Of course, the oxygen must be in stoichiometric excess relative to the low ignition point fuel so that there is sufficient oxygen present in the gaseous mixture to burn a portion of the carbonaceous stratum thereby driving unburned hydrocarbons from the stratumwhich are recovered thru the production borehole around which the ignition was initiated.

Low ignition point fuels which may be utilized in the process comprise, with their ignition points, carbon disulfide, 248 F.; propyl ether, 372 F..; benzaldehyde, 377 F.; and ethyl ether, 379 F. These fuels may be used alone or in admixture as the low ignition point fuel. Any readily vaporizable or natural gaseous fuel having an ignition point below about 400 F. is advantageous in the process. The amount of low ignition point fuel should be in the range of about 0.25 to about 7% (by volume) of the air-fuel mixture. Even 0.5% is quite effective in reducing the combustion temperature and in increasing the rate of advance of the combustion front.

The use of these low ignition point fuels is of peculiar advantage to the advance of the combustion front by inverse injection since the injected airfuel mixture does not pass thru hot stratum before arriving at the combustion front and all of the fuel is consumed in the leading edge of the combustion front, thereby contributing to the advance of the same thru the stratum and to a lower combustion temperature. The same gaseous mixture (air and fuel) do not have the same advantages in direct drive of the combustion front because in this type of process the injected gases pass thru the hot burned out area and the fuel is burned therein before arriving at the leading edge of the combustion front, thereby having the effect of increasing the temperature back of the combustion front and merely reducing the amount of oxygen available at the leading edge of the front.

A preferred method of operation comprises injecting a mixture of carbon disulfide and air thru a ring of injection wells surrounding a production well around which a combustion zone has been established in conventional manner. The production well, being the only well open to venting in the area, receives the injected gases or their products of combustion so that the mixture of CS and air pass to the combustion front and advance the same thru the stratum to the injection wells. The combustion process heats and drives hydrocarbons from the stratum into the production well from which they are recovered in conventional manner.

Another method of operation comprises injecting air thru an outer ring of injection wells and simultaneously injecting the low ignition point fuel, such as CS thru an inner ring of injection wells closer to the production well from which the combustion front originates. When the combustion zone arrives at or approaches the inner ring of injection wells, the injection of fuel therethru is terminated and the fuel is then injected thru the outer ring of wells along with the injected air, or the injection of air may be shifted to a more remote outer ring of wells and the process continued in the same manner. The inner ring of injection wells may be closed in or they may be utilized as production wells, as desired.

It is also feasible to inject air thru alternate wells in a ring of wells surrounding a central production borehole and inject the low ignition point fuel thru the other alternate wells in the ring so that the two gases intermix in the stratum in the vicinity of the combustion front and enter the front in admixture, thereby having the same general effect as in the other methods of operation.

It is also feasible to utilize the process of the invention U in a line drive well pattern wherein a line of production wells is flanked on each side by a line of injection wells as is conventional in the art. In this type of operation, the fuel and air may be admixed before injection or they may be injected in alternate holes or Wells of the line of injection wells on each side of the production wells.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessaiy limitations on the invention.

I claim:

1. A process for producing hydrocarbons from an undepleted carbonaceous stratum comprising igniting said stratum around a production well therein, thereby estabiishing a combustion zone adjacent said well; forming a combustible mixture of O -containing gas and a gaseous fuel having an ignition point below about 400 35., said being in substantial stoic'niornetric excess relative to said fuel gas; introducing said mixture to at least one area of said stratum spaced apart from said production well; passing said mixture into said combustion zone so as to burn said fuel in the leading edge thereof and move said zone thru said stratum countercurrently to the flow of said mixture, thereby producing hydrocarbons from said stratum; and recovering the produced hydrocarbons.

2. The process of claim 1 wherein said fuel gas corn prises carbon disulfide.

3. process of claim prises ethyl ether.

4. The process of claim 1 prises propyl ether.

5. The process of claim prises benzaldehyde.

6. The process of claim 1 wherein said fuel is in the range of 0.25 to 7 volume percent of the injected mixture.

1 wherein said fuel gas coinwherein said fuel gas com- 1 wherein said fuel gas coni- References Cited in the file of this patent UNITED STATES PATENTS 2,722,277 Crawford Nov. 1, 1955 2,793,696 Morse May 28, 1957 2,880,803 Parker Apr. 7, 1959 2,901,043 Campion et a1. Aug. 25, 1959 

1. A PROCESS FOR PRODUCING HYDROCARBONS FROM AN UNDEPLETED CARBONACEOUS STRATUM COMPRISING IGNITING SAID STRATUM AROUND A PRODUCTION WELL THEREIN, THEREBY ESTABLISHING A COMBUSTION ZONE ADJACENT SAID WELL; FORMING A COMBUSTIBLE MIXTURE OF O2-CONTAINING GAS AND A GASEOUS FUEL HAVING AN IGNITION POINT BELOW ABOUT 400*F., SAID O2 BEING IN SUBSTANTIAL STOICHIOMETRIC EXCESS RELATIVE TO SAID FUEL GAS; INTRODUCING SAID MIXTURE TO AT LEAST ONE AREA OF SAID STRATUM SPACED APART FROM SAID PRODUCTION WELL; PASSING SAID MIXTURE INTO SAID COMBUSTION ZONE SO AS TO BURN SAID FUEL IN THE LEADING EDGE THEREOF AND MOVE SAID ZONE THRU SAID STRATUM COUNTERCURRENTLY TO THE FLOW OF SAID MIXTURE, THEREBY PRODUCING HYDROCARBONS FROM SAID STRATUM; AND RECOVERING THE PRODUCED HYDROCARBONS. 